The present invention relates in general to a flextensional transducer and pertains, more particularly, to a directional flextensional transducer.
A number of so-called flextensional transducer designs have evolved based on the patents of W. J. Toulis, U.S. Pat. No. 3,277,433, "Flexural-Extensional Electromechanical Transducer", Oct. 4, 1966 and H. C. Merchant, U.S. Pat. No. 3,258,738, "Underwater Transducer Apparatus", June 28, 1966. In the invention of Toulis an oval-shaped cylindrical shell is driven along its major axis by a stack of piezoelectric bars resulting in a magnified motion of the shell in the minor axis as driven by the piezoelectric stack. The motions are opposite in phase and the magnification is approximately equal to the ratio of the major to minor axis if the shell is in the shape of an ellipse. In the H. C. Merchant invention the shell is curved inward in a concave way so that the motion along the major axis and the ends is in phase with the motion in the direction of the minor axis.
In the two above-identified patents to W. J. Toulis and H. C. Merchant, the two radiating surfaces are symmetrically arranged on each side of the driving member and consequently moved together, both outward or both inward. Because the radiating surfaces are generally used in environments in which they are small compared to the wavelength of sound in the medium, they are essentially omnidirectional radiators. However, there are situations in which radiation from only one surface is desired. For arrays of elements this inherent omnidirectional radiation or bidirectionality leads to a requirement for a baffle being placed behind the elements. However, this is expensive, and/or cumbersome.
Accordingly, it is an object of the present invention to provide a flextensional transducer that is directional having one side surface that moves with amplified motion while a major portion of the opposite side surface is essentially motionless or of a motion that is inefficient in sound radiation.
Another object of the present invention is to provide a directional flextensional transducer which is simultaneously driven in both odd and even modes so that acoustic radiation emanates mostly from one side only so that the transducer may be utilized in a directional application. In this way an array of these transducers may be used to send sound in one particular direction using one side, without the complications of back radiation from the second side.
For further background also refer to transducers described in U.S. Pat. No. 3,176,262 to S. L. Ehrlich and P. D. Frelich, and U.S. Pat. No. 3,732,535 to S. L. Ehrlich. The transducer in U.S. Pat. No. 3,176,262 is of cylindrical construction while the transducer described in U.S. Pat. No. 3,732,535 is of spherical design. These transducers operate in their extensional modes of vibration.
Still another object of the present invention is to provide a directional flextensional transducer that operates both in extensional and inextensional or bending modes of operation to provide a single-sided flextensional transducer. In accordance with the present invention a flexural shell mode and a particular oscillating body mode are co-excited, as described in further specific detail hereinafter, to produce this single sided flextensional transducer.